The present invention relates to well bore tools and, more particularly, to an apparatus for retrieval of metal debris, such as cuttings, shavings, and other foreign objects that accumulate in the process of perforating or milling over bridge plugs and other down hole obstructions from a well bore.
The oil and gas industry uses various types of bridge plugs that are installed in the annulus and often are covered in cement when the well is completed. Removal of these plugs often poses a problem for the industry. Conventionally, a rotary bit drills the cement and the plugs out, while some of the cuttings of the plugs are carried to the surface by circulating liquids.
Sometimes, a production packer needs to be removed together with a metal pipe that it surrounds. In those cases, milling tools with gravity fed boot baskets are used for retrieving pieces of metal debris from the well bore. After retrieval of the production packer, it may become necessary to run a conventional fishing magnet to retrieve additional junk and cuttings from down hole.
A conventional fishing magnet is mounted inside a housing that is lowered into a well bore. It is limited in the ability to retrieve cuttings in that its magnetization is restricted to the extreme bottom surface of the magnet. The fact that circulating fluids lift the cuttings away from the bottom surface of the magnet renders such conventional fishing magnets useless in this particular case.
Oftentimes, a boot basket is used for collecting cuttings that did not attach themselves to conventional magnets. A boot basket has small openings for catching these particles. Consequently, many large size pieces or very small pieces suspended in the circulating fluid are not trapped in the basket and remain in the well bore, hindering the production of oil.
Another solution for retrieving debris from a well bore is to lower a magnet to a down hole location in an effort to attract metal waste material from the well bore. One such example is shown in U. S. Pat. No. 3,637,033 issued on Jan. 25, 1972 to Mayall, entitled xe2x80x9cDrilling Apparatus.xe2x80x9d In the ""033 patent, the tool for collecting magnetic waste material has an inner and outer coaxial tubular members made of non-magnetic material. A plurality of magnets is located between the tubular members, with the axes of the magnets being parallel to the common longitudinal axis of the tubular member. The magnets are secured on the tubular member, and recesses are formed between the magnets parallel to the longitudinal axis. Each recess occupies the space between the adjacent sides of two magnets.
The outer tubular member in the ""033 patent is made of stainless steel, and strips of non-magnetic material are welded to the outer tubular member at the base of each recess. The magnets are enclosed by the outer tubular member to protect the magnets against forceful contact with shavings attracted by the magnets when the tubular member is rotated.
While this design works in many cases, it has been observed that the outer sleeve somewhat obstructs the magnetic flux of the magnets and reduces the amount of magnetic waste that is retrieved by the tool.
The present invention contemplates elimination of drawbacks associated with the prior art and provision of a well bore apparatus for removal of metal debris, such as cuttings, shavings and other foreign particles from a well bore.
It is, therefore, an object of the present invention to provide an apparatus for retrieval of metal cuttings and other debris from a well bore.
It is another object of the present invention to provide an apparatus for retrieval of metal debris with increased xe2x80x9ccatchingxe2x80x9d capacity of the tool.
It is a further object of the present invention to provide an apparatus for retrieval of metal debris from a well bore that protects the magnets, while creating additional areas where the cuttings can accumulate for retrieval to the surface.
These and other objects of the present invention are achieved through a provision of a metal debris retrieval tool that comprises a cylindrical tubular body with a through opening and a plurality of recesses formed on the tool body. Each recess receives a magnet assembly therein. Each magnet assembly comprises a magnet liner fitted into the recess and a magnet member placed on the liner and detachably secured on the tool body.
The magnet members are protected against direct impact with the metal particles by a magnet protector formed by an outwardly extending portion of the tool body. To take advantage of the residual magnetic force created by the magnets, a plurality of secondary debris settling areas are created on the tool body between a magnet member and a magnet protector of an adjacent magnet member.